Conventionally, a processing apparatus that is connected to a network and performs specific operation according to an externally entered processing request (hereinafter referred to as a network-compatible apparatus), such as an image forming apparatus, is so controlled as to transfer to power save mode (also known as low power consumption mode or sleep mode, for instance) in which power supply to such constituent parts (circuits) as a heater and clock oscillation, for instance, are interrupted for the sake of power savings if no external processing request signal is received for a specific period of time. Even in a state of such power save mode, part or the entirety of a communications section of the apparatus performing communication with external devices is kept operating to ensure that the apparatus which has been stopped to operate would be automatically returned to normal operating conditions according to an externally received signal. Here, external requests include an inquiry about the internal status of the network-compatible apparatus (i.e., a request for a response concerning the internal status), for instance, besides processing requests (e.g., a request for printing print data in the case of an image forming apparatus). Causing the apparatus to return from the power save mode to normal mode each time an inquiry about the internal status is received would become a hindrance to power savings.
To overcome the problem, Japanese Patent Application Publication No. 2001-345980 proposes an apparatus in which an communications section stores information about the internal status of the apparatus at the time of transfer to low power consumption mode, and when an inquiry about the internal status is received, the communications section returns a response to prevent the apparatus from unnecessarily returning to normal mode.
Also, Japanese Patent Application Publication No. 2000-165419 proposes a system in which, when a client apparatus transfers to sleep mode, the client apparatus notifies a server to which the client apparatus is connected via a network that the client apparatus is transferring to the sleep mode, and when the server monitoring the network detects a message to the client apparatus which is currently in the sleep mode, the server returns a response in lieu of the client apparatus according to previously stored information. In this case, the client apparatus is held in the sleep mode until the server detects a message which falls out of the previously stored information content, thereby preventing unnecessary returning to normal mode.
According to technology shown in Japanese Patent Application Publication No. 2001-345980, however, the communications section of each network-compatible apparatus must carry out an operation for judging whether the content of an externally received signal is a request (inquiry) which can be responded to without causing the apparatus to return to the normal mode as well as an operation for responding to the inquiry. As a CPU which requires relatively large power consumption must be kept operational for performing these operations, there has been a problem that it is impossible to achieve sufficient power savings.
According to technology shown in Japanese Patent Application Publication No. 2000-165419, on the other hand, a communications section or the like of a network-compatible apparatus must carry out an operation for judging whether the content of a received signal is a return command causing the apparatus to return to the normal mode from the server. Consequently, there has been a problem that a CPU must be kept operational for performing this judgment operation. In a case where the technology shown in Japanese Patent Application Publication No. 2000-165419 is applied to a star network, and not a bus network, employing a device for performing communication data routing control, such as a switching hub (hub, line concentrator), there can arise a case where a transmitted signal (data) addressed to each network-compatible apparatus is not transferred to (does not reach) the server depending on a connecting position of the server. Thus, there has been a problem that the connecting position of the server in the network is restricted. Star networks employing a hub (line concentrator) are widely used since the number of network-compatible apparatuses connected to the network can be easily increased and decreased, and therefore, restrictions on such widely used networks would pose a practical problem.
Accordingly, the invention has been made in view of the problems. It is an object of the invention to provide a line concentrator which can prevent a network-compatible apparatus from unnecessarily returning from power save mode to normal mode in response to an inquiry from another network-compatible apparatus and thereby reduce power consumption of the network-compatible apparatus during the power save mode as much as possible in a star network configured by connecting a plurality of network-compatible apparatuses via the line concentrator. It is a further object of the invention to provide network-compatible apparatuses connected to such a line concentrator and a communication system configured by those devices.